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(Left) Tubular specimens from Gale Crater, Mars. (Right) Tubular specimen from Endurance Crater, Meridiani Planum, Mars.

(Left) Tubular specimens from Gale Crater, Mars. (Right) Tubular specimen from Endurance Crater, Meridiani Planum, Mars.

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Hundreds of tubular and spiral specimens resembling terrestrial tube worms and worm tubes were photographed in the soil and atop and protruding from “rocks” on Sols 177, 199 and 299 in the vicinity of Endurance Crater, Meridiani Planum. Dozens of these putative “worms” and tubes are up to 3 mm in size. These tubular specimens display twisting, bend...

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... tubular formations resembling "worm tubes" and "tube worms" some with "caps" and "collars" protruding from stony matrix or tubes or laying upon the surface have been photographed in Meridiani Planum by the rover Opportunity Microscopic Imager in the area leading from Eagle Crater to and within Endurance Crater. Morphologically the Endurance Crater "worm tubes" with open apertures are similar to those photographed atop and possibly attached to sedimentary rock in the "Vera Rubin Ridge" area of Gale Crater (Figure 1). Those on "Vera Rubin Ridge" have been described as "ichnofossils" and possible indicators of biology (DiGregorio 2018;Baucon et al. 2020;Joseph et al. 2020a) vs "stick shapes" due, hypothetically, to erosion resistant mineral grains (Greicius 2019). ...
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... documented in this report, these specimens have the classic features of "tube worms," spiral worms, and "worm tubes" many of which congregate near, adjacent to or on the rims around holes in the ground that may have served as hydrothermal vents (Figures 4-16). Some species of terrestrial tube worms (spionid polychaetes) have paired antenna-like organs referred to as "palps" (Dupré & Brosolo 2010); and features similar to these have been observed among the "tube worms" of Endurance Crater ( Figure 17). ...
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... documented in this report, these specimens have the classic features of "tube worms," spiral worms, and "worm tubes" many of which congregate near, adjacent to or on the rims around holes in the ground that may have served as hydrothermal vents (Figures 4-16). Some species of terrestrial tube worms (spionid polychaetes) have paired antenna-like organs referred to as "palps" (Dupré & Brosolo 2010); and features similar to these have been observed among the "tube worms" of Endurance Crater ( Figure 17). In addition, shrimp-shaped ( Figure 18) and spiral-shaped "worms" (Figures 19, 20) and oval-shaped Martian specimens with appendages similar to the pleopods of crustaceans (Figure 4) have been observed in close proximity to the tubular structures of Endurance Crater. ...
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... species of terrestrial tube worms (spionid polychaetes) have paired antenna-like organs referred to as "palps" (Dupré & Brosolo 2010); and features similar to these have been observed among the "tube worms" of Endurance Crater ( Figure 17). In addition, shrimp-shaped ( Figure 18) and spiral-shaped "worms" (Figures 19, 20) and oval-shaped Martian specimens with appendages similar to the pleopods of crustaceans (Figure 4) have been observed in close proximity to the tubular structures of Endurance Crater. On Earth crustaceans are often observed in close proximity to tube worm colonies (Dupré & Brosolo 2010;MacAvoy et al. 2003;Li et al. 2020). ...
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... Earth crustaceans are often observed in close proximity to tube worm colonies (Dupré & Brosolo 2010;MacAvoy et al. 2003;Li et al. 2020). Morphological comparisons with terrestrial tube worms and their tubes also indicates a close similarity to the Martian tubes ( Figures 21-22) and the variety of "worms" photographed on the surface of Endurance Crater (Figures 23-25). Furthermore, there are specimens that resemble worms and tubes which have become mineralized and fossilized ( Figures 26-27) and attached to "rock-like" matrix within which and adjacent to what appear to be worm holes and small tubular specimens protruding outward from these holes--similar to rock-dwelling tube worms on Earth (Figures 28, 29). ...
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... documented in this report, these findings indicative of putative tube worms, worm tubes and associated biological communities (Figures 30, 31), support the hypothesis that Endurance Crater, and its surroundings, provided a salty marine-environment in which these and other organisms evolved and flourished ( Hynek et al. 2015;Squyres et al. 2004Squyres et al. , 2006). Moreover, the disposition and state of preservation of these specimens upon the surface--if they are in fact tube worms and worm tubes--is indicative of recent rapid evaporation of these briny waters; and leaves open the possibility that some of these Martian "tube worms" may be dormant; or, they were "pickled" by this salty brine. ...
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... Be they robust or mucous-based, fossilized tubes are often broken or only pieces remain, and these remnants may become highly mineralized. Many of the Martian tubular fossils may have been broken, or are partially buried in the soil (Figure 11, 22, 23). Therefore, it is impossible to make detailed, fine structure comparisons between what we presume to be fossils of Martian vs terrestrial tube worms. ...
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... is no obvious evidence of crystallization or mineralization in the majority of specimens; though what appear to be mineralized tubular formations attached to "rocks" were also photographed (Figures 26, 27). As pointed out by an anonymous referee, some of the tubular specimens jutting out from matrix (Figures 12, 15 ) may be mineralized formations; e.g. gypsum or jarosite crystals inter-grown within a pyrite or sulfur matrix. ...
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... of the ovoid specimens have appendages resembling the pleopods of crustaceans ( Figures 30, 31). There is no resemblance to micrometeorites or tektites. ...

Citations

... Specimens resembling algae [26][27][28][93][94][95][96], domical concentric stromatolites, lichens, fungi, [27][28][29]30,97], and tube worms [31][32][33][34]98] have been photographed by the NASAs Mars rovers. Of course, similarities in morphology are not proof of life. ...
... Spectral and geological-morphological observations of the Syrtis Major Volcanic Plains that include vent-like and conical-chimney-like structures [140] , supports the impact and magma scenarios. Likewise, evidence of "vents" and minerals associated with hydrothermal and tube worm-symbiotic activity discovered within Endurance Crater and surrounding outcrops [98,138] is consistent with both scenarios for the formation of hydrothermal vents. ...
... The lakes of Endurance Crater have also been described as a salty "brine" [106][107][108][109]. Brines and hydrothermal vents are a favored habitat of "tube worms" and their symbionts [152][153][154][155]. Vents/holes surrounded by tubular specimens have been observed within Endurance Crater, the latter of which have been tentatively identified as fossilized/mineralized tube worms and their tubes [98,138]. ...
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In the ancient and recent past, various niches on Mars were habitable and possibly inhabited by organisms that have evolved and adapted to extreme surface and subsurface environments. Habitability is promoted by the high levels of iron that promotes melanization of various organisms that protects against radiation. Glacial and water-ice below the surface provides moisture to organisms at temperatures below freezing due to salts in these ices and heat generated from anomalous thermal sources. Impact craters formed over 3.7 bya appear to be highly magnetized thus providing additional protection against radiation; and if initially hosting a large body of water may have triggered the formation of hydrothermal vents. Tube worms, sulfur-reducing and other chemoautotrophs have thrived and likely still inhabit subsurface aquifers within Endurance Crater which was formed over 3.7 bya, has hosted large bodies of water, and also has the mineralogy of hydrothermal vents and surface holes surrounded by tubular specimens. Formations resembling fossil tube worms have also been observed in the ancient lake beds of Gale Crater which was formed over 3.7 bya. A comparative quantitative analysis of the Gale and Endurance Crater tubular specimens provides additional confirmation for the tube-worm hydrothermal vent hypothesis.
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